During the first half of this year, 67 law enforcement officers in the U.S. were killed while on duty – a 31 percent increase over the same period last year.

California has had the most officer deaths. Texas, New York, Florida and Virginia have had 4 officer deaths, according to the National Law Enforcement Fund.

"Of the four officers killed in Texas – somewhat typical of the country – two of those were shot and killed," says Craig Floyd, the fund's chairman and CEO. He says the two other Texas fatalities were because of on-duty heart attacks.

"When you combine the conventional crime fighting with the war on terror, we’re asking our law enforcement officers to do more with [fewer] resources, which is often the case," Floyd says. "As a result that puts added stress on the officers."Floyd says the number of officer deaths across the country had been in decline in recent years, which is why he says he’s alarmed by the spike so far in 2014. He’s calling for more training and protection as well as time to exercise during the shift.